1. Field of the Invention
The present invention relates to a novel polypeptide which induces the interferon-.gamma. (hereinafter abbreviated as "IFN-.gamma.") production by immunocompetent cells.
2. Description of the Prior Art
It has been said that IFN-.gamma. is a protein which has antiviral-, antioncotic- and immunoregulatory-activities, and is produced by immunocompetent cells stimulated with antigens or mitogens. Because of these biological activities, IFN-.gamma. has been expected for use as an antitumor agent from the beginning of the finding, and studied energetically on clinical trials as a therapeutic agent for malignant tumors in general including brain tumors. IFN-.gamma. preparations now commercially available are roughly classified into 2 groups, i.e. natural IFN-.gamma.s produced by immunocompetent cells and recombinant IFN-.gamma.s produced by transformants prepared by introducing into microorganisms of the species Escherichia coli DNAs which encode the natural IFN-.gamma.s. In the above clinical trials, either of these IFN-.gamma.s is administered to patients as an "exogenous IFN-.gamma.".
Among these IFN-.gamma.s, the natural IFN-.gamma.s are usually produced by culturing established immunocompetent cells in nutrient culture media supplemented with IFN-.gamma. inducers to form the IFN-.gamma.s, and purifying the IFN-.gamma.s. It is known that the type of IFN-.gamma. inducers greatly influence on the IFN-.gamma. production yield, the facilitation of the IFN-.gamma. purification, and the safeness of the final products. Generally, mitogens such as concanavalin A (Con A), Lens culinaris, Phytolacca americana, endotoxin and lipopolysaccharide are used. These mitogens, however, have problems of their molecular- and quality varieties depending on their origins and purification methods, as well as difficulty of yielding in a desired amount and in a constant IFN-.gamma. inducibility. In addition, most of these mitogens induce unfavorable side effects when administered to living bodies, and some of them even show toxicity, so that it is substantially difficult to induce the IFN-.gamma. production by directly administering such mitogens to living bodies.